Chronic Total Occlusions (CTOs) are vascular lesions which are totally occluded and thereby inhibit normal blood flow. Such occlusions can occur anywhere in a patient's vascular system, arteries, and veins, including coronary vessels, as well as carotid arteries, renal arteries, cerebral arteries, arteries of the head and neck, iliac arteries, femoral arteries, popliteal arteries, and other peripheral arteries.
Typically, a CTO may be occluded for several weeks to several months, or longer. Such blockages can have serious medical consequences, depending upon their location within a patient's vascular system. For example, blockage of the coronary vessels that supply blood to the heart can cause damage to the heart.
Since most lesions form episodically over a long period of time, the ischemic tissue distal the lesion has time to form collateral circulation. In the case of coronary arteries, these collateral vessels can form from the proximal artery and connect into the distal artery (“ipsilateral collaterals”) or can form from the other major arterial branches and connect into the distal artery (“contralateral collaterals”). When the lesion finally becomes a total occlusion, the collateral circulation is typically sufficient to keep the distal tissue alive, though ischemic. In cardiac circulation, this ischemic tissue causes angina. Therefore, it is desirable to reestablish flow to the distal tissue.
Various surgical procedures are currently used to reestablish flow through or around the blockage in blood vessels. Such procedures include coronary artery bypass graft surgery and balloon angioplasty. Balloon angioplasty typically involves inserting a balloon catheter over a guidewire and into the occlusive lesion, expanding the balloon in the lesion, and if necessary, placing a stent in the now expanded lesion to keep it open.
Chronic total occlusions are more difficult to cross than partially occluded lesions because a guidewire must penetrate the lesion, rather than navigate a pre-existing lumen. Complications may result from these difficulties. For example, the distal end and tip of the guidewire may have insufficient support or rigidity to enter the lesion, causing the end to buckle. Or the guidewire may perforate the vessel, especially when the distal end and tip of the guidewire is not oriented towards the occlusion. If the guidewire has a pre-formed bend at the tip to assist in its initial orientation as it enters the occlusion, the internal lesion tissue may cause the guidewire to take an unwanted path within the occlusion. If the guidewire cannot successfully cross the occlusion, subsequent therapeutic devices, such as a balloon angioplasty catheter, cannot be advanced across the occlusion to dilate and treat it. Similar problems are encountered when attempting to cross an occlusion at a bifurcation. A guidewire having insufficient support or rigidity to enter the lesion will bend or, in some cases, perforate the vessel at the bifurcation.
For these reasons, the success rate for crossing and treating CTOs is much lower than that for partially occluded lesions, particularly for coronary CTOs. Furthermore, even when the total occlusion is successfully crossed with conventional guidewires, it often requires a great deal of time and skill on the part of the physician. Thus, there is a need for an improved system and method of crossing an occlusion.